1. Field of the Invention
The present invention relates to a hybrid integrated circuit device, and particularly, to a high-frequency power amplifier circuit device achieving high mechanical strength and improved heat radiation.
2. Description of the Prior Art
A conventional hybrid integrated circuit device (hereinafter referred to as the hybrid IC device) such as a high-frequency power amplifier circuit device has an insulation substrate for supporting circuit elements. The circuit elements include active elements such as ICs, transistors, and diodes, as well as passive elements such as resistors, capacitors, and coils. The substrate has on its bottom surface a conductive pattern, which is usually soldered to a metal flange. The metal flange radiates heat generated by the circuit elements and reinforces the breaking strength of a circuit board when the hybrid IC device is mounted onto the circuit board.
FIG. 1 shows an example of a conventional hybrid IC device.
An insulation substrate 41 is made of, for example, alumina. Circuit patterns 42 made of a thick copper film are formed on the substrate 41. Circuit elements are mounted on the substrate 41 and are electrically connected to the circuit patterns 42. The circuit elements include active elements such as resistors as well as passive elements such as transistors.
A metal flange 47 is soldered to a conductive pattern (not shown) formed on the bottom surface of the substrate 41. Clip-like lead terminals 43 hold terminals of the circuit patterns 42 and the metal flange 47 and are soldered together. The lead terminals 43 are fitted to a circuit board. The integrated circuit area on the substrate 41 is covered with a cap 46, to complete the hybrid IC device. The cap 46 is made from plastics or metal. The conductive pattern serves as a grounding pattern and its size is designed to attach the metal flange 47.
According to this prior art, the metal flange 47 will warp due to the difference between the thermal expansion coefficients of the substrate 41 and metal flange 47 that are soldered together. The warp disturbs heat radiation of the circuit elements and mechanically breaks the substrate 41 during heat cycle tests. Soldering the metal flange 47 to the substrate 41 is usually a separate process from mounting the circuit elements onto the substrate 41. This complicates and increases manufacturing processes.